1. Field of the Invention
The present invention relates to a substrate, a head, an apparatus and a method each for arranging a plurality of minute electroconductive balls, which are bonded to form bumps on the electrodes of a semiconductor element, printed circuit board (PCB), etc., wherein a means for recognizing whether or not balls are held is provided.
2. Description of the Related Art
In the ball bump process which is applied in producing a semiconductor device, bumps are formed of minute electroconductive balls on the electrode portion (pad) of a semiconductor device or a PCB, and these devices and PCBs are bonded via the bumps with each other. In such a process, a ball-arranging substrate is used, in which minute electroconductive ball-arranging holes are formed, corresponding to the location of electrodes of the semiconductor device or a PCB.
In the process for forming bumps, the minute electroconductive balls are sucked and held in the ball-arranging through holes of the ball-arranging substrate by means of vacuum suction, etc. It is necessary that a single ball is exactly sucked in a single hole of the ball-arranging substrate. If a ball is not sucked, then a bump is not formed on the electrode, and if two or more balls are sucked in a single ball-arranging hole, the bump may contact the adjacent pad.
As a method for recognizing such a ball-sucking failure, it is known to irradiate a laser beam from the lateral and the rear sides of the ball-arranging substrate. If an error is recognized, the error is removed by removing excess minute balls or repeating such a ball-suction. When it is recognized that the balls are arranged on the substrate without an error, the ball-arranging substrate with the balls as be are transported to a bump-bonding stage, where the locations of the minute electroconductive balls of the substrate and the electrode pads of a semiconductor device are aligned with each other.
After the completion of the alignment, the ball-arranging substrate, on which the minute electroconductive balls are sucked, is lowered down on the semiconductor device, and then the minute electroconductive balls and the electrode pads are bonded with each other by means of heat pressing. In the case when bumps are formed of a low melting point metal at the electrode portions of a PCB, it is general that a flux is applied to the electrode portions, and minute balls are arranged at the electrode portions and then reflowed.
As set forth above, the prior art inspection for excess balls or lack of sucked balls includes a method for inspecting excess balls or lack of balls by irradiating light from the front or lateral side of the ball-arranging substrate. If there is lack of a ball, the light irradiated from the front side of the substrate reaches, through the open ball-arranging hole, the light-receiver located on the rear side of the ball-arranging substrate, so that lack of a ball can be detected. If there are excess balls, the light irradiated from the lateral side of the substrate is shut out, and thus the light does not reach the light-receiver located on the opposite side of the ball-arranging substrate, so that excess balls can be detected. However, this method of inspection does not have reproducibility in recognizing defects of the balls and is not used, in industrial production, when the diameter of the balls is less than 300 xcexcm, particularly less than 200 xcexcm, because the amount of light and the accuracy of the location recognition are not sufficient.
On the other hand, another method using the image-recognization method is known for inspecting the arranged balls. According to the method, the light is irradiated to the minute balls, which are held on the ball-arranging substrate, and the reflected light is inspected by a CCD camera. The reflected light is converted to binary images, i.e., the light reflected by the balls is converted to white image, and the light reflected by the substrate is converted to black image. Thus, the ball-arranging condition is recognized.
However, it has been considered that it was difficult to exactly recognize the minute balls sucked and held-on the ball-arranging substrate by the image recognizing method and this method was not applied in the industry. For example, in the case when the ball-arranging substrate is made up of a metal, e.g. stainless steel, the light reflected at the substrate itself causes erroneous recognization e.g. due to reflections from machinery defect and damage portions or due to insufficient intensity difference between the light reflected by the minute balls and that reflected by the ball-arranging substrate itself causing an insufficient contrast. Also burrs may be formed on the substrate, when metal working, e.g., mechanical working, electrodischarging and laser irradiation is applied. In such a case, the accuracy was remarkably influenced when the minute balls, whose diameter was less than 200 xcexcm, were mounted on the chip, etc.
Furthermore, when the substrate used is made of glass, the irradiated light is transmitted through the glass and reaches the jig, which holds the glass substrate, and the light reflected by the jig causes errors in recognition of the balls as a metal arranging substrate does. That is, the transmitted light is irregularly reflected near the ball sucking hole to provide white bright images, causing the recognition of sucked balls to be uncertain. And the light is reflected by the defects scattered on the surface of the substrate, where the reflected light also gives white images. Such a reflected light may be erroneously recognized to be caused by the sucked minute balls.
The object of the present invention is to provide a ball arranging substrate, arranging head, arranging apparatus and arranging method, in which the conditions of sucked balls more precisely than before, by which ball bumps can be formed more exactly.
For example, as disclosed in Japanese Unexamined Patent Publication No. 4-250643, a conventional ball-arranging substrate is produced by forming ball-arranging holes on the substrate of a metal, e.g., stainless steel or a ceramic material, etc. by means of precise electrodischarging, laser-irradiation, electroforming, etching, etc.
When the ball-arranging substrate is a metal, e.g., stainless steel, misalignment is caused by thermal expansion of the arranging substrate during aligning between the ball-arranging holes and the electrodes due to a large difference in the thermal expansion coefficient between a metal substrate and silicon chip. When the ball-arranging holes are formed by means of laser irradiation or electrodischarging, a protuberance is formed around the holes and thus, dispersion of the height of sucked balls and a decrease in the sucking capability are observed. Furthermore, in the prior art it was difficult to precisely open the ball-arranging holes, of a diameter less than 100 xcexcm, by means of a general purpose working apparatus. If the diameter of the ball-arranging holes must be less than 100 xcexcm, the opened holes are narrowed by means of metal plating. However, the number of working processes is increased and the diameter of the opened holes is not formed uniformly, and the shapes of the holes are not formed as true circles. Thus, these defects result in misplacement of the arranged balls, and when bumps formed on a semiconductor device, or innerlead of TAB, or a printed circuit board, etc. are arranged at a narrow pitch, the precision of the ball arrangement is lowered.
Japanese Unexamined Patent Publication No. 7-95554, discloses a ball-arranging glass substrate. However, the disclosed substrate is not suitable for arranging minute electroconductive balls.
Another object of the present invention is to provide a ball-arranging substrate, a ball-arranging head, and an apparatus for arranging balls and also a method for arranging balls, in which the minute balls are arranged more precisely than before, and thus ball-bumps. are formed more exactly.
In order to achieve the object set forth above, the present invention provides the following:
(1) A ball-arranging substrate comprising:
a substrate having a main surface; and
a plurality of ball-arranging holes which are provided on said main surface at locations corresponding to those of the electrodes of a semiconductor device or a printed circuit board, etc., for sucking and holding minute electroconductive balls in said ball-arranging holes;
wherein when light illuminates the ball-arranging surface with said sucked minute electroconductive balls, to optically recognize the conditions of arrangement of said minute electroconductive balls by means of the light reflected by said minute electroconductive balls and by said ball-arranging surface, the wavelength of said light emitted by a light source is selected in the range of 300 to 900 nm, and the reflectivity of said ball-arranging substrate for light from said light source is not more than 50%, provided that a reflective mirror may be provided on the rear surface of said ball-arranging substrate opposite to said light source, in the case when said ball-arranging substrate is transparent to the irradiated light.
(2) A ball-arranging substrate according to said (1), wherein a anti-reflection film is formed on said ball-arranging surface on which said minute electroconductive balls to be sucked and held.
(3) A ball-arranging substrate according to (1) or (2), wherein said ball-arranging substrate is made of glass.
(4) A ball-arranging substrate according to (3), wherein said substrate is made of photosensitive glass.
(5) A ball-arranging substrate according to anyone of (1) to (4), wherein the ratio of the diameter of said ball-arranging holes on the side of minute electroconductive ball-arrangement to the diameter of said minute electroconductive balls is in the range of from 1/3 to 4/5; and,
the thickness of said ball-arranging substrate is in the range of from 0.3 to 1.0 mm.
(6) A ball-arranging substrate according to (1) to (5), wherein the diameter of said minute electroconductive ball is in the range of 20 to 200 xcexcm.
(7) A ball-arranging substrate according to (1) to (6), wherein said reflectivity of said ball-arranging substrate is not more than 30%.
(8) A minute electroconductive ball-arranging glass substrate comprising: a plurality of ball-arranging holes, the diameters of which are smaller than those of said minute electroconductive balls, for arranging said minute electroconductive balls at locations corresponding to those of the electrodes of a semiconductor device or a printed circuit board,
wherein the ratio of the diameter of said ball-arranging holes to that of said minute electroconductive balls is in the range of from 1/3 to 4/5, the diameter of said ball-arranging holes being measured on the surface of said minute electroconductive ball-arranging glass substrate; and the thickness of said minute electroconductive ball-arranging glass substrate is in the range of from 0.3 to 1.0 mm.
(9) A minute electroconductive ball-arranging glass substrate according to (8), wherein said ball-arranging glass substrate is made of photosensitives glass.
(10) A minute electroconductive ball-arranging head, comprising:
a minute electroconductive ball-arranging substrate in accordance with (1) to (9); and,
a means for holding minute electroconductive balls, provided with a vacuum space for sucking said minute electroconductive balls, on the other surface of said substrate opposite to the surface holding the minute electroconductive balls.
(11) A minute electroconductive ball-arranging apparatus comprising:
a minute electroconductive ball-arranging head in accordance with (10);
light sources for illuminating the electroconductive balls holding surface of said ball arranging substrate;
a light-receiver for receiving light reflected by said ball arranging substrate after being emitted from said light sources; and,
an image-recognizing and treating means for recognizing the conditions of the arrangement of said minute electroconductive balls on said ball-arranging substrate, based on the output from said light-receiver, said image-recognizing and-treating means examining the conditions of arrangement of said electroconductive balls after said electroconductive balls are arranged on said ball-arranging substrate.
(12) A ball-arranging apparatus accordance with (11), wherein the arrangement of the electroconductive balls on said ball-arranging substrate is repeated again if the conditions of the arrangement of the electroconductive balls are found to be inappropriate as a result of said examination.
(13) A method for arranging balls comprising the steps of:
sucking and holding to arrange minute electroconductive balls on a surface of a minute electroconductive ball-arranging substrate, corresponding to the locations of the electrodes of a semiconductor device or a printed circuit board; and
illuminating said surface, on which said minute electroconductive balls were sucked, and recognizing conditions of arrangement of said minute electroconductive balls using the light reflected by said minute electroconductive balls and that reflected by said minute electroconductive ball-arranging surface,
wherein the wave length of a light source is set in a range of 300 to 900 nm, and the reflectivity of the light from said light source by the minute electroconductive ball-arranging surface, is made not more than 50%.
(14) A method for arranging minute electroconductive balls according to (13), wherein said ball-arranging substrate is in accordance with (1) to (9).